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AggregateFunction

fsqlite_func::aggregate

Trait AggregateFunction 

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pub trait AggregateFunction: Send + Sync {
    type State: Send;

    // Required methods
    fn initial_state(&self) -> Self::State;
    fn step(&self, state: &mut Self::State, args: &[SqliteValue]) -> Result<()>;
    fn finalize(&self, state: Self::State) -> Result<SqliteValue>;
    fn num_args(&self) -> i32;
    fn name(&self) -> &str;
}
Expand description

An aggregate SQL function (e.g. SUM, COUNT, AVG).

This trait is open (user-implementable). Extension authors implement this trait to register custom aggregate functions.

§State Lifecycle

  1. initial_state creates a fresh accumulator.
  2. step is called once per row.
  3. finalize consumes the state and returns the result.

§Send + Sync

The function object itself is shared across threads via Arc. The State type must be Send so it can be moved between threads.

Required Associated Types§

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type State: Send

The per-group accumulator type.

Required Methods§

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fn initial_state(&self) -> Self::State

Create a fresh accumulator (zero/identity state).

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fn step(&self, state: &mut Self::State, args: &[SqliteValue]) -> Result<()>

Process one row, updating the accumulator.

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fn finalize(&self, state: Self::State) -> Result<SqliteValue>

Consume the accumulator and produce the final result.

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fn num_args(&self) -> i32

The number of arguments this function accepts (-1 = variadic).

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fn name(&self) -> &str

The function name, used in error messages and EXPLAIN output.

Implementors§